"Our 1 million followers are connected to over 43 million people on LinkedIn, roughly one-quarter of the entire LinkedIn population,” says Natalie Malaszenko, vice president of digital marketing for HP.

HP grew its LinkedIn followers in a couple of ways. For instance, CEO Meg Whitman has just begun to write for LinkedIn's "Influencers" series, where big names write columns exclusively for LinkedIn members. She's generated about 29,000 followers after posting two columns this week, one on HP's turnaround, and another on her change of heart about gay marriage.

More importantly, HP has been using targeted LinkedIn Follow ads, which encourage users to subscribe to HP updates which appear when they log in to the professional network. Those have helped it add 300,000 followers in two months, according to LinkedIn vice president of marketing Nick Besbeas.

This isn't the largest social media following HP has. Its Facebook page has nearly 2.3 million fans. But HP's LinkedIn presence has more than five times the number of Twitter followers @HP has—180,000.